1. Field of the Invention
The present invention relates to a driver assistance system of a vehicle including at least one ultrasonic sensor for ascertaining the distance of the vehicle from an obstacle, the sensor being supplied with electrical energy by an onboard electrical system of the vehicle. Furthermore, the present invention relates to a method for operating a driver assistance system of a vehicle including at least one ultrasonic sensor for ascertaining the distance of the vehicle from an obstacle, the sensor being supplied with electrical energy by an onboard electrical system of the vehicle.
2. Description of the Related Art
Ultrasonic sensors used in driver assistance systems for ascertaining the distance of the vehicle from an obstacle operate using the pulse-echo principle for distance measurement. An ultrasonic pulse is initially generated by the ultrasonic sensor, and the propagation time of the ultrasonic pulse to an obstacle and of the echo back to the sensor is then ascertained. By evaluating the propagation time, it is possible to calculate the distance from the obstacle. During the generation of an ultrasonic pulse, the ultrasonic sensor has a very high power consumption. On the other hand, during the ultrasound reception phases, the power consumption of the sensor is very low. The ultrasonic sensor is supplied with electrical energy via the onboard electrical system.
In the event of a sudden undervoltage in the onboard electrical system of the vehicle, for example, triggered by an automatic start-stop system, two basic strategies of driver assistance systems and responses of the ultrasonic sensor are known:
In a first variant, there is no response by the sensor to the occurrence of an undervoltage in the onboard electrical system of the vehicle. Subsequently, the high consumption of power and current results in a sharp voltage drop at the sensor. As a result of the remaining supply voltage at the ultrasonic sensor being too low, a reset of the sensor is carried out. As a result, the ultrasonic distance measurement is interrupted. All functions of the driver assistance system which are based on the distance measurement and the ultrasound data receive no further distance information. This results in a severe degradation of the system.
In a second known strategy, in the event of an undervoltage in the onboard electrical system of the vehicle, the ultrasonic sensor completely prevents transmission pulse generation after detection of an undervoltage by the sensor. Consequently, the ultrasonic distance measurement is corrupted due to the ultrasonic pulse which is not generated, since no further signal echoes are detectable and it is no longer possible to calculate the distance of the vehicle from an obstacle. All those functions of the driver assistance system which operate based on the distance measurement and the ultrasound data no longer receive any distance information. Thus, this also results in a severe degradation of the system.
A method for controlling the energy distribution in a motor vehicle is known from published German patent application document DE 198 29 150 A1, a hierarchical control structure being used which distinguishes between higher-level and lower-level components. The load power for a certain lower-level component is provided only if the higher-level components are already being supplied. Furthermore, the lower-level components are deactivated if the higher-level components have a demand for power output. In the event of an undervoltage, it is disadvantageous that the hierarchically lower-level ultrasonic sensor is completely deactivated and is thus not able to provide any further distance information. This approach also results in all functions of the driver assistance system which operate based on the distance measurement and the ultrasound data not receiving any further distance information, resulting in a severe degradation of the system.
The object of the present invention is thus to refine a driver assistance system and a method for operating a driver assistance system of a vehicle including at least one ultrasonic sensor for ascertaining the distance of the vehicle from an obstacle in such a way that the availability of ultrasound-based driver assistance systems is increased in the event of an undervoltage in the onboard electrical system of the vehicle.